The long term objectives of this research proposal are to delineate cellular and molecular mechanisms of action involved in photodynamic therapy (PDT) and to evaluate methods for enhancing the efficacy of PDT. Clinical use of PDT continues to produce promising responses, and controlled Phase II and Phase III trials of PDT using Photofrin II (dihematoporphyrin-ether) have been initiated under the sponsorship of the Lederal Division of American Cyanamid. Enthusiasm for PDT continues to grow, but information related to basic in-vitro and in-vivo mechanisms associated with PDT needs to be obtained in order to fully evaluate the clinical potential of this modality. Cellular procedures will be utilized in isolating PDT resistant tumor cell strains. These cell strains will subsequently be used for molecular, biochemical and cellular characterization studies as well as for evaluating in-vivo PDT responses. A comprehensive evaluation of PDT sensitivity of cellular components of the vasculature will be performed utilizing cloned human and bovine cells. PDT Induces the over expression of oxidative stress proteins and this property will now be exploited in order to document in-vivo PDT target sites in treated tumors. In this regard, in-situ hybridization (using cDNA's to stress protein genes) will be performed in order to document the sites and kinetics of PDT induced oxidative stress protein mRNA expression. In-vivo procedures will also be utilized to study the adjunctive use of the hypoxic cell cytotoxin (SR-4233) with PDT. Quantitative tumor and normal tissue responses will be documented as a function of drug doses, light doses and time intervals between injections and treatments. New photosensitizers with photochemical and photobiological properties which appear to be superior to Photofrin II are available for basic research, and thereforee, both Photofrin II (the porphyrin undergoing current clinical evaluation) and new photosensitizers (such as chlorins and phthalocyanines) will be investigated in this proposal.